docs: Move examples that are more like test cases to the new tests/ directory; add better example configurations (#3069)

* chore: Move examples that are more like test cases to the new `tests/` directory

* chore: Stash

* feat: Add better examples for EKS managed node groups

* chore: Add better examples for self-managed node groups

* chore: Update docs and correct `nodegroup` to `node group`

tests/user-data/templates/al2023_custom.tpl

@@ -0,0 +1,15 @@
+%{ if enable_bootstrap_user_data ~}
+---
+apiVersion: node.eks.aws/v1alpha1
+kind: NodeConfig
+spec:
+  cluster:
+    name: ${cluster_name}
+    apiServerEndpoint: ${cluster_endpoint}
+    certificateAuthority: ${cluster_auth_base64}
+    cidr: ${cluster_service_cidr}
+  containerd:
+    config: |
+      [plugins."io.containerd.grpc.v1.cri".containerd]
+      discard_unpacked_layers = false
+%{ endif ~}